Remove dependency on tiny-emitter

[kikuomax]

Description

mockTableColumn uses tiny-emitter to emulate now obsolete $on and $off APIs. See https://v3-migration.vuejs.org/breaking-changes/events-api.html#event-bus
How about to replace tiny-emitter with our own implementation.

Why Buefy need this feature

tiny-emitter looks abandoned and having issues with TypeScript and ESM. So we should migrate from it before it would become a debt.

[wesdevpro]

https://v3-migration.vuejs.org/breaking-changes/events-api.html

3.x Update
We removed $on, $off and $once methods from the instance completely. $emit is still a part of the existing API as it's used to trigger event handlers declaratively attached by a parent component

[wesdevpro]

I claim this task.